Preparation of fluorocarbons



United States Patent C) 3,278,406 PREPARATION OF FLUOROCARBONS William A. Mod, Lake Jackson, Gerald Peltier, Danbury,

and William R. Von Tress, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, Mich.,

a corporation of Delaware N Drawing. Filed Sept. 7, 1962, Ser. No. 222,208

6 Claims. (Cl. 204-463) This invention relates to a method for preparing fluorocarbons and more particularly is concerned with a process for preparing per fluorinated hydrocarbons by reacting chlorine with methylene fluoride (OF H at low temperatures in the presence of visible or ultra-violet light.

Presently, perfluorinated hydrocarbons such as tetrafluoroethylene (C 1 for example, are prepared by pyrolyzing chlorodi-fluoromethane (OF ClH) at temperatures of from about 600 C. to about 700 C. In this process the rate of conversion of the chlorofluoromethane per pass must be kept low, for example about 27% per pass, to prevent undesirable carbon formation and other undesirable side reactions. :In this present commercial process, therefore, for economical operation a considerable amount of unreacted chlorofluoromethane reactant must be separated from the product gases and recycled.

Other methods propose that tetrafluoroethylene can be prepared by high temperature pyrolysis of trifluoromethane at temperatures of from about 1500 to about 2500 C. by means of electric are devices and hot graphite tube reactors.

=N-ow unexpectedly it has been found in the process of the instant invention that formation of tetrafluoroethylene and other per'fluorinated and fluoro-substituted hydrocarbons readily can be accomplished by reacting together chlorine and methylene fluoride in the presence of visible or ultra-violet light radiation to give a high conversion of methylene fluoride at relatively low temperatures of from about 40 C. to about 450 C.

It is a principal object of the present invention to provide a low temperature process for preparing perfluorinated hydrocarbons wherein the conversion of the methylene fluoride reactant is as high as about 98% of theoretical.

It is another object of the present invention to provide a low temperature method for preparing perfluorinated hydrocarbons, such as tetrafluoroethylene, which method eliminates or minimizes the need for use of costly materials of construction in the reactors.

It is another object of the present invention to provide a method for preparing tetra-fiuoroethylene wherein the amount of unreacted methylene fluoride starting material is minimal in comparison with that obtained in present commercial processes thereby making the separation of such reactant material from the product mass a relatively easy process.

It is still a further object of the present invention to provide a process for preparing readily separated fluorocarbon products having considerable commercial importance.

These and other objects and advantages will be apparent from the detailed description presented hereinafter.

In the instant process, chlorine and methylene fluoride, i.e. difluoromethane, are reacted at a temperature of from about 40 to about 45 0 C. in the presence of ultra-violet or visible light at a chlorine to methylene fluoride volume ratio of from about 0.75 to about 1.5 and a residence time of the reaction mixture at the reaction temperature of from about 0.01 to about seconds. Preferably the reaction temperature is from about 100 to about 400 C. and the residence time of the reaction mixture at the re- 3,278,406 Patented Oct. 11, 1966 action temperature is from about 0.5 to about 1 second. In operation with ultra-violet light irradiation, a chlorine to difluoromethane volume ratio of from about 0.75 to about 1.0 preferably is employed. With visible light irradiation, a volume ratio of about 1.0 is preferred. The term visible light as used herein refers to light radiation having a wave length of from about 4000 to about 7000 A. Ultra-violet light radiation suitable for use in the present process is that having a wave length from about 4000 down to about 2000 A.

Visible light sources suitable for use as a reaction promoter or catalyst in the instant process include sunlight GE w. T8 /2 bulb and the like. Ultra-violet light sources which have been found to be effective include, for example, GE H100A4 Hg lamp, GB 300 \v. VA3 bulb, GEF ISTS BLB bulb, and the like.

The instant process can be carried out on a batch, continuous or cyclic type process. Preferably, however, the process will be carried out on a continuous basis wherein the gaseous reactants are injected simultaneously into a heated reaction zone and the product materials recovered at the exit of the heated area. For such operation a tube furnace preferably is employed. The instant process, however, can be carried out utilizing any of a wide variety of conventional heated reactor vessels, furnaces and the like as known to one skilled in the art.

The materials of construction to be employed in the reactor for the instant process are not critical except that these have the necessary structural and physical characteristics to stand up under the reaction conditions. Also, these should not be reacted upon in an undesirable manner by the reaction materials or the products of the reaction. Conveniently high strength glass or glass lined vessels are employed.

With glass reactors, if a glass transparent to ultra-violet and visible radiation is used, e.g. a Vycor quartz glass, the irradiation source can be positioned outside the reactor.

Although the instant process is employed primarily to obtain tetrafluoroethylene, other useful compounds simultaneously are co-produced from the reaction of chlorine and methylene fluoride by the practice of the present method. These products include, for example, hexafluoropropene, dichlorotetrafluoroethylene, dichlorodifluoroethylene and monochlorodi-fluoromethane.

The penfiuoroand partially fluorinated materials produced by the instant process find utility, for example, as refrigerants, aerosol propellants, intermediates for polymers, electrical insulation, etc.

The following examples will serve to illustrate further the present invention but are not meant to limit it thereto.

EXAMPLE 1 A Vycor quartz glass air-cooled tube about 12 inches long having an internal diameter of about 8 mm. was placed near a ultra-violet irradiation source. This source exposed about a 2 inch length of the tube. A thermocouple Was taped to the outside of the tube wall. The ultra-violet irradiation source was activated and a mixture of methylenefluoride and chlorine was fed to the reactor. The gases were passed through a premixing tube to blend these before they entered the reactor. The product gases exiting from the reactor tube were passed through a water-cooled condensor.

A number of runs were made wherein the reaction temperature was controlled at a predetermined temperature. For each of these runs, prdouct gas samples (200- 500 ml.) were collected after the reactor temperature had become stabilized at that selected for a given run.

The gas samples were analyzed by vapor phase chromatography and infrared spectroscopy. Table I, which follows, tabulates the data and results obtained from this series of tests. Reactant conversion and-product yield were calculated from the analytical data.

the present invention without departing from the spirit or scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

Table I Reactants Product Yield Run Contact Reactor CFzHz No. Time, Temp, Conv.,

CF HZ, C12, Clz/CFzHz, sec. 0. percent C2F4 03F CFzClz C2F4Clz CFzHCl cc./miu. cc./min. vol. ratio 800 795 0. 99 0. 06 170 85. 4 2s. 2 8 18.2 1 48. 0 1,310 1, 275 0.98 0.03 232 84.9 30.1 o 9 17.7 1 4 46.4 410 405 U. 99 O. 102 83. 6 29. 3 0 6 16. 4 2 2 48. 9 230 230 1. 0 0. 29 70 88. 1 2G. 0 0 9 19. G 1 9 49. 4 135 110 o. 82 0. 57 45 54. 5 10. e Tr 13. 2 1 a 72.8

EXAMPLE 2 The same procedure and apparatus was employed as described for Example 1 except that a visible light source (a GE 100 w. T8 /2 electric bulb) was employed as activator instead of the ultra-violet irradiation device. Table II summarizes the data and results from this test.

EXAMPLE 3 The same procedure was followed as described for The coil tube reactor described in Example 3 was used along with a visible light irradiation source in a number of runs evaluating the efiect of Cl /CF H volume ratio on product yield. Table IV presents the results of this series of tests.

Various modifications can be made in the process of Table III summarizes the results of 30 We claim:

1. A process for preparing fiuorocarbons which comprises:

reacting chlorine and methylene fluoride for a. period of from about 0.01 to about 10 seconds at a temperature of from about to about 450 C. in the presence of light radiation of wave length from about 7000 A. to about 2000 A., and at a chlorine/methylene fluoride volume ratio of from about 0.75 to about 1.5.

2. A process for preparing fiuorocarbons which comprises:

(a) providing a reaction mixture of chlorine and methylene fluoride, said mixture having a chlorine/methylene fluoride volume ratio of from about 0.75 to about 1.0,

(b) introducing said mixture into a reactor maintained at a temperature of from about 100 to about 400 C.,

(c) reacting said reaction mixture in said heated reactor for a period of from about 0.5 to about 1.0 sec-- 0nd in the presence of a reaction promoter selected from the group consisting of visible light radiation and ultraviolet light radiation having a wave length of from about 7000 A. to about 2000 A., and

Table II Reactants Product Yield Run Contact Reactor CFzHz o. ime, Temp., Conv.,

CFzHz, Clz, CIz/CFzHz, Sec. C. percent CgF CgFu CFzCl: CzFqClz CFzHCl ccJmin. ccJmin vol. ratio 1, 310 1, 275 0. 98 O5 88. 7 Tr. 0 8. 1 0 91. 9 800 795 0. 99 0. 08 r 87. 7 0 0 7. 5 0 92. 5 410 405 0. 99 0. 14 78. 9 Tr. 0 20. 5 11. 1 67. 8 230 230 1. 0 0. 25 120 84. 3 21. 3 0. 6 18. 5 2. 2 53. 3 110 0. 82 54 G0 74. 5 30. Q 1. 1 19. 2 3 0 43. 4

Table III Reactants Product Yield Run Contact Reactor CFQH} No. Time, Tcrnp., Conv.,

CFgHz, l Olz/OFzH-z, 590- 0. percent C11 4 C3Fa CFgClz C2F4C12 CFzH Cl ccJmLu cc./min vol. ratio 1, 310 660 0. 51 O. 8 225 55. 0 O 0 5. 0 0. 4 94. 2 1, 310 1. 000 0. 76 0. 7 260 79. 1 30. 3 0. 4 13. 3 Nil 54. 7 1, 310 1, 300 0. 99 0. 6 270 87. 0 35. 4 2. 0 20. S 10. 6 25. 2 1, 310 1, 645 1. 26 0. 5 310 98. 7 29. 7 11. 3 30. 5 5. 6 12. 3 1, 310 1, 990 1. 52 O. 4 34.0 99. 0 25. 3 2. 5 41. 6 3. 2 2. 4

Table IV Reactants Product Yield Run Contact Reactor CFzHa No. Time, Tcmp., Conv.,

CFgHz, C12, Clz/CFzHz, sec. 0. percent C F C F CF 0]; 02F4C1g OF HCl ccJmin cc./min. vol. ratio 1, 310 660 0. 51 0. 9 200 '16. 5 0 0 4. 1 0 95. 9 1, 310 1, 000 0. 76 0. 7 265 72. 0 D 0 7. 0 0 93. 1 1, 310 1, 300 0. 99 0. 5 325 S9. 3 45. 5 2. 1 2A. 6 2. 1 22. 1 1, 310 1, 645 1. 26 0. 4 375 98. 0 19. 4 8. 0 43. 8 4. 4 5. 8 1, 310 l, 990 1. 52 0. 3 430 98. 3 35. 6 2. 3 37. 0 2. 6 2. 5 1, 645 1, 645 1. O 0. 4 410 89. 6 46. 9 3. 0 19. 9 1. 5 19. 6

5 6 (d) removing the fluorocarbon containing products (a) introducing a reaction mixture of chlorine and from the reaction zone. methylene fluoride into a reactor maintained at from 3. A process for preparing tetrafluoroethylene which about 60 to about 430 C. in the presence of visible comprises: light radiation, said reaction mixture having a chlo- (a) introducing a reaction mixture of chlorine and 5 rine/methylene fluoride volume ratio of from about methylene fluoride into a reactor maintained at a 0.8 to about 1.5, temperature of from about 70 to about 340 (3., in (b) maintaining said reaction mixture in said reactor the presence of ultraviolet radiation having a minifor a residence time of from about 0.25 to about 0.5 mum wave length of about 2000 A., said reaction Second, an

mixture having a chlorine/methylene fluoride vol- 10 removing The tetl'afluoroethylene containing P ume ratio of from about 0.75 to about 1.5, mass from Said P (b) maintaining said reaction mixture in said reacto The Process as defined clalm 5 Wherem the reacfor a residence time of from about 0.03 to about tion is carried out continuously in a tube-type reactor 0 8 Second and which is transparent to visible light radiation.

(c) removing the tetrafluoroethylene containing pro References Cited by the Examiner uct mass from said reactor. 7

4. The process as defined in claim 3 wherein the re- UNITED STATES PATENTS action is carried out continuously in a tube-type reactor 3,073,220 2/1963 Cassatt et a1 which is transparent to ultraviolet radiation. 20 JOHN H M ACK Primary Examiner 5. A process for preparing tetrafluoroethylene which comprises: H. S. WILLIAMS, Assistant Examiner. 

1. A PROCESS FOR PREPARING FLUOROCARBONS WHICH COMPRISES: REACTING CHLORINE AND METHYLENE FLUORIDE FOR A PERIOD OF FROM ABOUT 0.01 TO ABOUT 10 SECONDS AT A TEMPERATURE OF FROM ABOUT 40* TO ABOUT 450*C. IN THE PRESENCE OF LIGHT RADIATION OF WAVE LENGTH FROM ABOUT 7000 A. TO ABOUT 2000 A., AND AT A CHLORINE/METHYLENE FLUORIDE VOLUME RATIO OF FROM ABOUT 0.75 TO ABOUT 1.5. 